Fox executives had every reason to beat Brazilian drums and blow whistles this morning as the studio’s feature toon Rio exceeded expectations with a $40 million estimate – the best three-day opening in 2010, waltzing past Rango’s $38.1 million. Following behind in second was Dimension’s Scream 4 with $19.3 million, a figure that fell below the industry’s low-20s expectations (some even thought it could fetch $27 million). While Scream 4’s haul is financially sound for the Weinsteins’ books given its $40 million cost, the return is anticlimactic among franchise reboots, even if the last chapter was 11 years ago. Scream 4 might have a better fate abroad (numbers out tomorrow) where it saw a No. 1 bow in the United Kingdom and France, and second place in both Brazil and Russia.

Roadside Attraction’s The Conspirator not only cracked into the top 10 with $3.92 million but inched out Universal’s clunker comedy Your Highness for ninth place.

Breaking down the specifics on why Rio won the weekend is easy: Fox and it’s go-to toon house Blue Sky built Rio as a global winner, forging specific marketing tie-ins (Rovio’s Angry Birds Rio app game) and ancillaries (Sergio Mendes soundtrack) which were true to the film’s spirit and heightened its profile in a competitive family moviegoing market. Fox wisely locked in a calendar slot that could build steam through Easter spring break and remain a May family offering until the arrival of Kung Fu Panda 2 on Memorial Day.

And an added bonus: “It’s G-rated, which means anybody can go,” said Fox’s senior distribution v.p. Bert Livingston. “It’s the start of summer and this should get everyone in the habit of going to the movies.” Rio drew mostly moms (53% of attendees) and 50/50 over and under 25. “But everyone can go to this film. You don’t need a kid,” said Livingston.

For a Blue Sky non-sequel/franchise title, Rio did swell, charting below the first Ice Age ($46.3 million) and above Robots ($36 million). Overseas, where Blue Sky’s Ice Age sequels have outperformed domestic by three to four times, Rio has grossed an astounding $128 million to date. “It’s working in every country on earth,” beamed Livingston. Working strongly in Rio’s favor abroad is its Latino pride themes, which is already giving the film a heartier playability abroad than Blue Sky’s Robots ($132.5 million) and Horton Hears a Who! ($142.6 million overseas).

Weinstein Co. is pleased enough with Scream 4’s opening to likely crank out more chapters. But this opening was lackluster by both horror reboot and four-quel standards. Sure, the film was expected to bow behind Scream 3 ($34.7 million) and Scream 2 ($32.9 million). However, there was a lack of “want to see.” even though Dimension held all the Scream parts in place (director Wes Craven, screenwriter Kevin Williamson, and the original cast).

Scream 4’s opening ranks below last April’s A Nightmare On Elm Street ($32.9 million), which headlined unknowns and had been was asleep for seven years. Scream 4 even slotted below such April horror resurrections as 2005’s The Amityville Horror ($23.5 million) and 2008’s Prom Night ($20.8 million), as well as 2007’s Saw IV ($31.8 million) (consecutive annual sequel releases aside). The critics didn’t help Scream 4 as they split further over the last three days at 58% rotten. Granted big city critics weren’t going to be onboard with a horror film; many felt that Scream’s satirical shenanigans have grown long in the tooth. But when the horror-philes feel that the sequel to a beloved horror franchise is “straight out of a TV series” – that’s troubling indeed.

The original Scream was a breath of fresh air to the horror genre, both in plot and its iconoclastic Christmas 1996 release. FearNet boldly suggested that “someone in the boardroom” should have said, “screw the formula, kill the stars in Act I, and run off in some crazy new direction,” an approach that would have kept the spirit of the first Scream when it blithely offed its poster girl Drew Barrymore in the first minutes of the film.

With more kids unleashed from school (80% are off on Good Friday and 30% this week), Scream 4 may avoid the precipitous drop that curses most horror films in their second frames. The film’s questionable B- Cinemascore cast doubts on the film’s long term run. On the upside for both Scream 4 and Insidious: It looked like moviegoers were making a double feature of the two titles Friday with the FilmDistrict title placing third behind Scream 4’s second. Clearly, the under 25 demo came back to the multiplex for Scream 4, which attracted 54% of that crowd; mostly women (52%).

Elsewhere among adults, Conspirator reaped a 44% spike between Friday and Saturday and continues to sell out matinees across the country.